Cardiopulmonary arrest with apnea and loss of palpable pulse (CA) in childhood is a tragic event that very often results in either death or poor quality long-term neurological survival. Recent randomized clinical trials (RCT) in adult populations have reported improved neurologic outcome and survival in groups that received short term mild hypothermia following out of hospital ventricular fibrillation (VF) arrest. The efficacy of hypothermia in children following cardiac arrest is not known. CA in children is commonly secondary to a respiratory etiology that results in hypoxia, which after a period of time results in cardiac arrest. Asystole or pulseless electrical activity are the most common presenting cardiac rhythms when resuscitation is initiated. In adults by contrast, a sudden cardiac event (without a preceding period of hypoxia) most often occurs with VF or ventricular tachycardia, the common presenting rhythms. In this clinical trial planning grant application, 15 Pediatric Emergency Care Applied Research Network (PECARN) children's hospitals with intensive care units will obtain pilot data from the medical records of patients who have sustained a CA with return of spontaneous circulation in either the outpatient or inpatient setting. Characterization of this population will include arrest specific events and etiology, patient characteristics, hospital course, interventions received, hospital survival, and neurologic outcome. This information will be used to create inclusion and exclusion criteria, and to calculate sample size requirements for a future RCT of hypothermia following pediatric cardiac arrest. Duration of time to successfully enroll patients from this cohort of 15 children's hospitals for a future RCT will be estimated. This application will also result in creation of multiple documents needed to perform a RCT of hypothermia after cardiac arrest in childhood including study related data forms, study protocols, manuals of operation, institutional review board and informed consent related documents, and other materials. The PECARN will support all phases of this application with its existing clinical trials research infrastructure that includes a steering committee, five clinical trials supporting subcommittees, and a central data management coordinating center (CDMCC). The CDMCC will make operational all data and analysis related tasks of this application, and assure all study sites are compliant with regulations concerning data security and confidentiality.